Sampling device

ABSTRACT

An improved centrifuge sampling device for the capture and size segregation of particles less than 2 microns in diameter from a fluid containing same. The device comprises a rotating body and cap which define a spirally shaped conduit having from 1.5 to about 2.5 convolutions. The particulate-laden fluid as sampled is split by the sampler into a large stream and a small stream. The large stream is directed to the beginning of the spiral conduit where entrained particles are removed by centrifugal forces. The smaller stream is introduced into the larger stream contained in the spiral conduit when substantially all particulate matter has been removed from the larger stream and the flow has been rendered laminar.

United States Patent [191 Anderson SAMPLING DEVICE Paul L. Anderson,Pleasanton, Calif.

Kaiser Aluminum & Chemical Corporation, Oakland, Calif.

Filed: Nov. 20, 1972 Appl. No.: 307,772

Inventor:

Assignee:

US. Cl. 73/28, 73/432 PS, 55/270 Int. Cl. GOln 15/00 Field of Search...73/28, 421.5 R, 424, 432 PS;

References Cited UNITED STATES PATENTS FQREIGN PATENTS OR APPLICATIONS740,128 11/1955 Great Britain 209/135 July 16, 1974 PrimaryExaminer-Richard C. Queisser Assistant ExaminerStephen A. KreitmanAttorney, Agent, or FirmPaul E. Calrow; Edward J.

Lynch 5 7] ABSTRACT An improved centrifuge sampling device for thecapture and size segregation of particles less than 2 microns indiameter from a fluid containing same. The device comprises a rotatingbody and cap which define a spirally shaped conduit having from 1.5 toabout 2.5 convolutions. The particulate-laden fluid as sampled is splitby the sampler into a large stream and a small stream. The large streamis directed to the beginning of the spiral conduit where entrainedparticles are removed by centrifugal forces. The smaller stream isintroduced into the larger stream contained in the spiral conduit whensubstantially all particulate matter has been removed from the largerstream and the flow has been rendered laminar.

9 Claims, 2 Drawing Figures PATENTEDJUU s 1914 SHEET 2 6F 2 FIG.2

SAMPLING DEVICE BACKGROUND OF THE INVENTION This invention relates to adevice for sampling the particulate matter in a fluid stream rangingfrom about 0.05 to 2.0 microns in size.

Of late, there has been considerable interest in the sampling andanalysis of air-borne particles below 2 microns in size. Medicalevidence has tended to show that the particles below 2 microns tend tobe the most damaging to human health. Moreover, it is well known thatparticles below 2 microns often account for the dirty look to the airover a large city. Generally, particles greater than 2 microns in sizesettle readily and therefore the sampling and size segregation of theparticles can be accomplished by conventional means. I-Iowever, thecapture and particularly the size segregation of particles below 2microns in size is very difficult.

Cascade inertial impactors are frequently used to capture and segregateaccording to size particles less than 2 microns in diameter. However,the efficacy of these devices is extremely low below a particle size of0.8 micron. This loss in efficiency is due primarily to there-entrainment of the small particles from stage to stage. Also, withthese devices, the small particles tend to agglomerate on impact,preventing any optical post mortem evaluation of the particle size andshape.

Particles from about 5 to 0.5 microns in diameter have been analyzedwith a centrifuge spectrometer, such as that described by Stober (seeEnviron. Sci. Technol. 3, l,280-l,296 (1969). Similar centrifugespectrometers by Moss et al. and Cotrapa et al. are described in anarticle in IEEE Transactions on Nuclear Science, Vol. 'NS19, No. 1,February, 1972, by Otto G. Raabe entitled, Instruments and Methods forCharacterizing Radioactive Aerosols. These devices generally comprise acentrifuge rotor which has aspiral' duct in the upper surface thereof.The aerosol sample is drawn by negative pressure into the duct throughan inlet slit at the axis of rotation of the rotor and near the innerwall of the duct where it meets a laminar stream of clean air. The rotoris spun rapidly by suitable means and the aerosol particles move acrossthe clean air stream and collect on the outer wall of the channel inaccordance with their aerodynamic diameters. These centrifuges are notuseable as portable field devices because of their large size, andbecause they require a separate clean air source. Moreover, due to thecoriolis forces characteristic of these centrifuges, segregation ofparticles below about 0.6 micron is poor.

Hockrainer in Interface Science, Vol. 36, No. 2, June, 1971. page 191,described an improved centrifuge spectrometer. With this device, theaerosol sample is aspirated into the spectrometer through an aperturelocated in the cap at the axis of rotation of the rotor. The aerosolstream is split into large and small streams. The larger stream isdirected through a conduit in the rotor to a circular conduit on theouter portion of the rotor. As the large aerosol stream passes throughthe first half of the circular conduit, it is cleansed of theparticulate matter and the gas flow is rendered laminar. The smalleraerosol stream is introduced into the second half of the conduit wherethe gas is clean and the flow is laminar. The particulate matter in thesmall stream is forced to the outer walls of the conduit in accordancewith its aerodynamic diameter and is deposited thereon. While this is anefficient device for sampling aerosol-containing gases, the particlesize range for this instrumentis very small unless the radius of the.rotor is increased considerably. A radius of up to about BRIEFDESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of thesampler of the present invention.

FIG. 2 is a top view of the rotor body of the present invention with therotor cap removed.

DESCRIPTION OF THE INVENTION The present invention provides for animproved centrifuge sampler which can be used as a portable device inthe field and moreover can capture and efficiently segregate a broadspectrum of particle sizes ranging from about 0.05 to 2 microns inaerodynamic diameter.

The centrifuge spectrometer of the present invention comprises arotating, spirally shaped groove or conduit having from about 1.5 toabout 2.5 convolutionsThe first section of the spiral conduit isessentially a cleaning and laminating section so as to provide a clean,laminar gas flow to the second or sample-capturing section. The rotationof the unit causes the aerosol to be sampled to be aspirated into thecentrifuge unit. The aerosol is then split into large and smallfractions. The larger aerosol stream is directed to the first section ofthe spiral channel or conduit where the particulate matter containedtherein is removed and the flow is rendered laminar. The smaller aerosolstream is then introduced into the clean, laminar gas flow in the secondsection where the particulate matter in the smaller stream is caused toflow by centrifugal force across the clean laminar gas flow and depositon the outer surfaces of the conduit in accordance with its equivalentaerodynamic diameter. By placing a collector strip on the outer surfacesof the second'section of the conduit, the collected particles can thenbe removed and the particles morphology and chemistry can be studied bysuitable means, such as scanning electron microscopy and X-ray methodswithout particle removal and the resuspension or particle agglomerationcharacteristic of the prior art devices. The coriolis forces in thepresent invention are minimal and therefore the size segregation iseffective to below 0.1 micron.

As used herein, the expression equivalent aerodynamic diameter or termsof similar import refer to the diameter of a sphere of unit densitywhich has the same terminal velocity as the particle in question in theidentical accelerating field and carrying gas. All reference herein toparticle diameter or size refers to the equivalent aerodynamic diameter.

With reference to FIGS. 1 and 2 which illustrate an embodiment of thepresent invention, the centrifuge spectrometer comprises a rotor body 10and a rotor cap 11 affixed thereto. The rotor body and cap define aspirally shaped channel or conduit 12 which has from at least 1.5 toabout 2.5 convolutions with a gradually increasing radius. As indicatedin the drawing, the start of the spirally shaped conduit is disposedaway from the axis of rotation of the rotor. A co-extensive aperture 13is provided in the rotor body 10 and cap 11 for the aspiration of theaerosol to be sampled. Means such as conduits l and 16 are provided tosplit the aerosol stream into a large and a small stream, respectively.The larger stream is directed to the start of the spiral groove throughconduit 15. Conduit l6 directs the smaller aerosol stream into thesecond half of the first complete convolution of the spiral channel 12.For highly effective cleaning and laminating, the smaller aerosol streamshould be introduced toward the end of the first complete convolution asshown in the drawing. Preferably, the angle 6 between conduits 15 and 16is from about 3" to about 30. Aperture 17 is provided at the end of thespiral conduit 12 to allow for the exiting of the combined gas streamfrom the sampling unit. The rotor cap 11 can be suitably affixed to therotor body such as by the threaded connection. Drive shaft 20 isprovided on the lower surfaces of the rotor body to facilitate rotationof the unit during operation. Although the groove 12 is shown in thedrawings as being disposed in the rotor body 10, the groove can readilybe disposed in the rotor cap 11. As indicated in the drawing therotation of the unit is in the direction of the spiral groove.

In operating this spectrometer, the body is rotated by suitable means ata rate of about 2,000 to 20,000 revolutions per minute. The rotation ofthe unit draws the aerosol to be sampled through aperture 13 and intothe body of the rotor wherein it is split into a large and a smallstream. The larger gas stream is directed to the beginning of thespirally shaped channel or groove and while this aerosol travels throughthe first convolution, the particulate matter therein is forced againstthe outer walls of the channel or groove and a clean laminar gas flow isgenerated. The smaller aerosol stream is introduced into the second halfof the first convolution of the spirally shaped conduit or channel. Theparticulate matter in the aerosol is caused to pass through the laminarclean air flow in accordance with its equivalent aerodynamic diameterand deposit on the outer walls of the remaining portion of theconvoluted channel or groove. Preferably a sampler strip, such asaluminum foil, Mylar strip or the like, is positioned on the tionsdepending upon the particulate size range desired.

The volume ratio of the large aerosol stream to the small aerosol streamranges from about 20:1 to about 5:1. It is preferred to introduce thesmaller aerosol toward the end'of the first convolution to allow for thet substantially complete removal of particulate matter from the largergas stream to thereby avoid any contamination with the particulatematter in the smaller aerosol stream which is captured in the samplingsection of the spiral channel or conduit.

Depending upon the rotational speed of the rotor body of thespectrometer unit and the orifice size in the entry and exit apertures.the gaseous flow rates from about 2100 milliliters per second can beobtained. In accordance with the present invention, the spiral channelwidth ranges from about 0.2 to 1.5 centimeters and the depth ranges fromabout 0.5 to 3.0 centimeters. 1f desried, the width of the channel canbe gradually increased from the beginning to the end of the conduit. Thediameter of the spectrometer ranges from about 2 to about 6 inches.Above 6 inches, the unit is too large to be of any value as a portablefield unit and below about 2 inches, no useful range of particulatesizes can be captured. For eflicient size separation, the rotationalspeed of the rotor must be controlled within fi percent, preferablywithin :1 percent.

To avoid blockage of the entry aperture and unnecessarily large entrylosses, it is advisable to pretreat the aerosol to remove particlesabove 2 microns in diameter. A suitable pretreating device is a cascadeinertial impactor.

In the table below, examples given which illus trate embodiments of thepresent invention. The data illustrate the effect of variations ofprocess parameters and conduit dimensions on the effective range ofparticulate capture. In all of the examples, the spiral conduit had twocomplete convolutions. A greater effective range could be obtained byextending the length of the spiral conduit. The inside radius is theradius of the inner wall of the spiral conduit at the start and finishof the sampling section of the conduit.

Width of Example No. Ht. of Conduit Inside Radius of Flow Rate Vol.Ratio of Rotor Speed Effective Range cm Conduit cm Conduit cm ml/secLarge to Small rpm microns Stream 1 2.0 0.5 3.60 to 4.75 25 10/1 10,0000.10-1.2 2 2.0 0.5 3.60 to 4.75 20 10/1 10,000 008-10 3 2.0 0.5 3.60 to4.75 15 10/1 10,000 007-09 4 2.0 0.5 3.60 to 4.75 10 10/1 10,000 004-075 2.0 0.5 3.60 to 4.75 25 10/1 7,500 0.15-1.6 6 2.0 0.5 3.60 to 4.75 2510/1 10,000 0.101.2 7 2.0 0.5 3.60 to 4.75 25 10/1 12,500 006-0.) 8 2.00.5 3.60 to 4.75 25 10/1 15,000 005-07 9 2.0 0.5 1.50 to 2.00 25 10/110,000 030-19 10 2.0 0.5 2.30 to 3.00 25 10/1 10,000 0.151.5 11 2.0 0.53.00 to 4.00 25 10/] 10,000 0.12l.3 12 2.0 0.5 3.80 to 5.00 25 10/110,000 0.101.l 13 1.0 0.5 3.60 to 4.75 25 10/1 10,000 0.161.5 14 2.0 0.53.60 to 4.75 25 10]] 10,000 0.10-1.2 15 3.0 0.5 3.60 to 4.75 25 10]]10,000 0.081.0 16 2.0 0.5 2.20 to 2.90 16 10/1 10,000 0.151.5

outer surfaces of the channel so as to capture the particles and renderthem amenable to analysis, such as by scanning electron microscopy andX-ray chemical analysis. The length of the channel for the samplingsections ranges from at least 16 to about 1% convo1u- Although theinvention is described in terms of removing particulate matter from agaseous stream, the

invention can be efficiently employed in removing particulate matterbelow 2 microns in diameter from a liquid medium, such as in a hydrosol.

It is obvious that various modifications and improvements can be made tothe present invention without departing from the spirit thereof and thescope of the appended claims.

What is claimed is:

l. A sampling device for capturing and segregating particulate matterhaving an equivalent aerodynamic diameter from about 0.05 to about 2.0microns from a fluid containing same comprising:

is positioned on the outer surface of said spirally disposed conduit.

5. The device of claim 1 wherein means to split said fluid into largeand small streams provide a volume ratio of large to small streams fromabout 5:1 to about 20:1.

6. The device of claim 1 wherein the width of said spirally disposedconduit is gradually increasing.

7. A method of capturing and segregating particulate A. a generallycylindrically shaped member having a 10 matter having an equivalentaerodynamic diameter rotor body and a rotor cap, said body and capdefining a generally spirally shaped conduit having from about 1.5 toabout 2.5 convolutions, the radius of said conduit gradually increasingand the beginning of said conduit being disposed a distance away fromthe axis of rotation of said rotor body and cap;

B. means to introduce said fluid stream into said cylindrically shapedmember;

C. means to split said fluid into small and large streams;

D. means to introduce said large fraction into the beginning of thefirst convolution of said spirally disposed conduit;

E. means to introduce said smaller fraction into the second half of thefirst convolution of said spirally shaped conduit;

F. means to exhaust said combined large and small fractions from saidconduit; and

G. means to rotate said cylindrically shaped member.

2. The device of claim 1 wherein said rotor body is from about 2 toabout 6 inches in diameter.

3. The device of claim 1 wherein the spirally disposed conduit has agenerally rectangular shaped cross section with a width from about 0.2to about 1.5 centimeters and a depth of about 0.5 to 30 centimeters.

4. The device of claim 3 wherein a thin collector strip from about 0.05to about 2.0 microns from a fluid containing same comprising:

A. splitting said fluid into a small and large fraction, the volumeratio of large to small stream ranging from about 5:1 to 20:1;

B. passing said larger fraction through at least onehalf convolution ofa rapidly rotating, spirally shaped conduit to generate a laminargaseous flow therein and to remove substantially all particulate matterfrom said larger fraction;

C. introducing said smaller fraction into said larger fraction after theflow of said larger fraction has become essentially laminar andsubstantially all particulate matter has been removed therefrom;-

D. passing said combined streams through at least one completeconvolution of said rapidly rotating, spirally shaped conduit to removeand segregate according to size said particulate matter having anequivalent aerodynamic diameter of about 0.05 to about 2.0 microns; and

E. discharging said combined streams.

8. The method of claim 7 wherein said conduit is rotating from about2,000 to 20,000 revolutions per second.

9. The method of claim 7 wherein the total flow of fluid into saidspirally shaped conduit ranges from about 2 to milliliters per second.

1. A sampling device for capturing and segregating particulate matterhaving an equivalent aerodynamic diameter from about 0.05 to about 2.0microns from a fluid containing same comprising: A. a generallycylindrically shaped member having a rotor body and a rotor cap, saidbody and cap defining a generally spirally shaped conduit having fromabout 1.5 to about 2.5 convolutions, the radius of said conduitgradually increasing and the beginning of said conduit being disposed adistance away from the axis of rotation of said rotor body and cap; B.means to introduce said fluid stream into said cylindrically shapedmember; C. means to split said fluid into small and large streams; D.means to introduce said large fraction into the beginning of the firstconvolution of said spirally disposed conduit; E. means to introducesaid smaller fraction inTo the second half of the first convolution ofsaid spirally shaped conduit; F. means to exhaust said combined largeand small fractions from said conduit; and G. means to rotate saidcylindrically shaped member.
 2. The device of claim 1 wherein said rotorbody is from about 2 to about 6 inches in diameter.
 3. The device ofclaim 1 wherein the spirally disposed conduit has a generallyrectangular shaped cross section with a width from about 0.2 to about1.5 centimeters and a depth of about 0.5 to 30 centimeters.
 4. Thedevice of claim 3 wherein a thin collector strip is positioned on theouter surface of said spirally disposed conduit.
 5. The device of claim1 wherein means to split said fluid into large and small streams providea volume ratio of large to small streams from about 5:1 to about 20:1.6. The device of claim 1 wherein the width of said spirally disposedconduit is gradually increasing.
 7. A method of capturing andsegregating particulate matter having an equivalent aerodynamic diameterfrom about 0.05 to about 2.0 microns from a fluid containing samecomprising: A. splitting said fluid into a small and large fraction, thevolume ratio of large to small stream ranging from about 5:1 to 20:1; B.passing said larger fraction through at least onehalf convolution of arapidly rotating, spirally shaped conduit to generate a laminar gaseousflow therein and to remove substantially all particulate matter fromsaid larger fraction; C. introducing said smaller fraction into saidlarger fraction after the flow of said larger fraction has becomeessentially laminar and substantially all particulate matter has beenremoved therefrom; D. passing said combined streams through at least onecomplete convolution of said rapidly rotating, spirally shaped conduitto remove and segregate according to size said particulate matter havingan equivalent aerodynamic diameter of about 0.05 to about 2.0 microns;and E. discharging said combined streams.
 8. The method of claim 7wherein said conduit is rotating from about 2,000 to 20,000 revolutionsper second.
 9. The method of claim 7 wherein the total flow of fluidinto said spirally shaped conduit ranges from about 2 to 100 millilitersper second.